JPH06103943A - Ion source by electron cyclotron resonance - Google Patents

Abstract

PURPOSE: To optimize an ion source by electronic cyclotron resonance by installing a tubular piece movable in parallel to a dielectric pipe in the peripheral part of the dielectric pipe. CONSTITUTION: An optimizing apparatus which optimizes an ion source comprises a tubular piece 47 known as a magnetic screw and the piece 47 is installed in the peripheral part of a first dielectric pipe 21 at a proper idle gap about 0.5mm from the pipe 21, so that friction at the time when the pipe 21 moves relatively and parallel to a housing 11 is avoided. Moreover the piece 47 has the same thickness as that of the housing 11 and is provided with a thread ridge, which can be squeezed into a tap-formed of the housing 11, in its peripheral part and the piece 47 is made movable by screwing/unscrewing of the piece 47 in the housing 11. Since the piece 47 is made of iron, high magnetic field grading exists in the level of the housing 11 and the position of the resonating point C can be controlled and at the same time the electric field at the point C can be optimized by high gas pressure and consequently, an ion source in a low ionization-charged state can be optimized.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to improved electron cyclotron resonance (ECR) ion sources, and more particularly to ion sources that allow the generation of multiply charged ions.

[0002]

BACKGROUND OF THE INVENTION Ion sources are used in many ways depending on the thermodynamic energy values of the generated ions, especially in ion and microetching applications, and scientific and medical applications. Can be used as an accelerator for particles.

In the electron cyclotron resonance ion source, a gaseous medium composed of one or more metal vapors or gases is used by using electrons highly accelerated by electron cyclotron resonance in a chamber closed like a high frequency cavity. Ions are obtained by ionizing. This electron cyclotron resonance is obtained by the combined action of a high frequency (HF) electromagnetic field injected into a chamber containing a gas to be ionized and a magnetic field existing in the chamber,
The amplitude B of the magnetic field satisfies the electron cyclotron resonance condition of the following equation. B = f · 2πm / e where e is the charge of the electron, m is its mass, and f is the frequency of the magnetic field.

In these ion sources, the amount of ions is as follows: first, a phenomenon in which an electron collides with a neutral atom forming a gas to be ionized to form an ion; and second, a neutral atom. Due to the competition between the two phenomena with the phenomenon of destroying these ions by recombination of them either alone or collectively when they collide. The neutral atoms originate from the gas which is not yet ionized and also on the chamber wall due to the collision of ions with the chamber wall.

This drawback is avoided by confining the ions formed in the chamber forming the ion source with the electrons used to ionize said ions. This is accomplished by creating radial and axial magnetic fields within the chamber, defining a "magnetic" surface that is not in contact with the walls of the chamber and is associated with satisfying electron cyclotron resonance conditions. This surface is in the shape of a rugby ball. The closer this isomagnetic surface is to the wall of the chamber, the more effective it is because the abundance of neutral atoms and hence the amount of ion / neutral atom collisions can be limited. Furthermore, this surface can confine ions and electrons generated by the ionization of the gas. Due to this confinement, the generated electrons can hit given ions a plurality of times to completely ionize them.

An ion source of this type was filed on Mar. 13, 1986 in the name of the Applicant, FR-A-25.
It is described in the document published by No. 95 868.

FIG. 1 schematically shows a prior art ion source. This ion source includes a chamber 1 and constitutes a resonance cavity that can be excited by a high frequency (HF) electromagnetic field. This electromagnetic field is generated by the electromagnetic field generator 3 and introduced into the chamber 1 by the waveguide 5 and the transition cavity 20.

Furthermore, the ion source is provided with an externally shielded magnetic structure (7, 9, 11), the sheath 11 of which allows only the space useful for electron cyclotron resonance in the chamber 1 to be magnetized. .

In addition to the outer casing 11, this magnetic structure is provided with a permanent magnet 7 and a solenoid 9 arranged around the chamber 1 to generate a magnetic field in the radial direction and a magnetic field in the uniaxial direction.
Have and. These two magnetic fields are superposed and distributed in the whole chamber 1. Therefore, they form a composite magnetic field, which defines the resonance isomagnetic surface 13 in the chamber 1.

The magnetic axis 15 is also in the long axis direction of the ion source, and has two openings 17 and 1 arranged in the outer package 11.
Ions can be extracted from the chamber 1 by traversing the exterior 11 via 9 and an electromagnetic wave and a gas or solid sample can be introduced.

Dielectric first and second pipes 21 and 2
3 shows the openings 19 of the exterior 11 and the openings 25 of the transition cavity 20.
And 27. These openings 25 and 27
Are located on the sides of the transition cavity 20 having the shape of a cube.

These two pipes 21 and 23 have a diameter relationship capable of matching with a coaxial line having a characteristic impedance of about 85Ω. This coaxial line preferably carries an electromagnetic transverse wave mode (TEM). In this mode, the electromagnetic field E is transverse to the direction of propagation of the radio wave and perpendicular to the surface of the conductor or pipe 21, 23.

To ionize the gas, said gas is introduced into the chamber 1 by means of a gas pipe 30 connected to the opening 27 of the transition cavity 20. The gas and electromagnetic waves introduced into the transition cavity 20 are transferred to the first and second pipes 21 and 2
3 is transferred to chamber 1. First pipe 21
The role of is to propagate the electromagnetic wave into the chamber 1 and inject it along the magnetic axis 15.

In the chamber 1, the introduced gas can be completely ionized due to the relationship between the electromagnetic field and the axial magnetic field. The generated electrons are highly accelerated by electron cyclotron resonance, resulting in the formation of a plasma of hot electrons confined within the volume confined by the resonance isomagnetic surface 13.

The ions thus formed in the chamber 1 are extracted from the chamber 1 by the extraction electric field generated by the potential difference applied between the electrode 31 and the chamber 1. Both the electrode 31 and the chamber 1 are connected to the power supply 33, and the electrode 31 is arranged outside the opening 17 of the chamber 1.

In order to control the intensity of the ionic current, it is possible to control the average power of the electromagnetic field by controlling the pulse generator 35 located in front of the power source 37 connected to the electromagnetic field generator 3. it can. The pulse generator 35 controls the power supply 37 by adjusting the run cycle, ie the ratio between the length of one pulse and the duration of the pulse.

Furthermore, the total pressure measuring means 39 is connected to the input of the comparator 41, the output of which is connected to the valve 43 of the gas pipe 30. The reference voltage R is applied to the second input of the comparator 41 and compared with the measured value of the ionic current to obtain the value to be transferred to the valve 43 at the output of the comparator 41. The valve 43 can control the amount of gas introduced into the chamber 1 to automatically adjust the ion current.

Furthermore, a third opening 2 on the side surface of the transition cavity 20 is provided.
An adaptive piston 45 connected to 9 makes it possible to adjust the internal volume of the transition cavity 20. The adjustment of the adaptive piston 45 is used to tune all the internal volume of the transition cavity 20 to the frequency of the electromagnetic waves and minimize the reflected waves, ie the electromagnetic waves returning to the electromagnetic field generator 3. When these internal volumes are tuned to the frequency of the electromagnetic waves, the electromagnetic waves injected by the electromagnetic field generator 3 into the transition cavity 20 are transferred to the chamber 1 containing the plasma, substantially through the pipes 21, 23. Absorbed by the magnetic surface 13 such as resonance

In the prior art ion source, the second pipe 2
3 is transparent to electromagnetic waves at its end portion 23a.
This end portion 23a is adjacent to the opening 19 of the chamber 1 located on the opposite side of the sheath 11.

In the inner space of the transparent end portion 23a, there is an axial magnetic field generated by the solenoid 9, an electromagnetic field and a high gas pressure. This electromagnetic field is generated by the electromagnetic wave transferred between the first pipe 21 and the non-transparent portion 23b of the second pipe 23, and the second pipe 2
3 through the transparent end portion 23a. For this reason, electron cyclotron resonance can be generated in the transparent end portion 23a of the second pipe 23 in the space where a high gas pressure is present. The higher the density of the plasma generated by electron cyclotron resonance in the transparent end portion 23a, the better the propagation of electromagnetic waves, and this high density plasma becomes one conductor. Furthermore, the plasma cord has the same outer shape as the portion 23b of the second pipe 23. Therefore, the characteristic impedance of the coaxial line does not change, and the reflection of electromagnetic waves can be prevented.

The end portion 23a, which is transparent to this electromagnetic wave, thus constitutes a self-regulated preionization stage. Here, as long as the electron cyclotron resonance zone is composed of the resonance magnetic surface 13, the excessive electromagnetic wave incident power propagates without being reflected.

[0022]

Therefore, in order to optimize the ion source as described in the prior art, firstly, the internal volume of the transition cavity 20 is adjusted by controlling the adaptive piston 45. And secondly,
It is necessary to adjust the strength of the current in the solenoid 9. These adjustments, if performed by an experienced operator, can take a very long time.
They may not achieve optimum ion source performance for hours, even days, in practice. In fact, these adjustments do not follow the known rules used to optimize the ion source.

[0023]

The present invention provides a magnetic structure having a chamber containing an ion plasma formed by electron cyclotron resonance and electrons, and a magnetic structure having an exterior. An outer enclosure surrounding the chamber, forming two radial and axial magnetic fields in the chamber to enclose a plasma in the chamber, and one transition cavity connected to an electromagnetic wave generator, First and second dielectric pipes connecting a chamber and a transition cavity, said first and second dielectric pipes having a transition portion opposite said sheath, said second pipe resonating at a particular point. An object of the present invention is to provide an apparatus for optimizing an ion source by electron cyclotron resonance including a second dielectric pipe, the resonance point in the second dielectric pipe. The moved and are provided with the means to optimally adjust the position of the resonance point.

The means for moving the resonance point preferably comprises a tubular piece arranged around the second pipe at the level of the transparent part and movable parallel to the pipe.

According to a preferred embodiment, the tubular piece is threaded on its outer periphery to form a screw and nut structure with the sheath.

Other features and advantages of the invention will become more apparent on reading the following description, given by way of illustration and not limitation with reference to the drawings.

[0027]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Generally, a standing wave exists on one coaxial line through which a TEM mode propagates, as described above, because of the reflection of the propagating electromagnetic wave. Due to the electromagnetic wave E, the standing wave is a voltage wave. Therefore, the two pipes 21 and 2
There are continuous voltage nodes and antinodes between 3 and 2.
The distance between one node or two antinodes is equal to 1/2 wavelength of the electromagnetic wave injected into the ion source.

In this ion source, there are three prominent points A, B and C of the magnetic axis 15. These three points A, B
And C have electron cyclotron resonance (ECR) conditions. That is, (E1) ω _HF = ω _{ce In} other words, the pulse of the electromagnetic wave HF has the same value as the electron gyro magnetic pulse, that is, the “electron cyclotron” pulse, and is expressed as follows. (E2) ω _ce = e / mB _r where e is the electron charge, m is the mass, and Br is the value of resonance induction.

Therefore, at points A, B and C of the node,
The following equation derived from (E1) and (E2) can be expressed as | Br | = (e / m) ω _HF .

In the case of the ion source described above, points A and B represent the ends of the resonance isomagnetic surface 13, also known as a closed resonance surface located in a confined plasma. Point C is located at the level of the second dielectric pipe 23 in the preionized plasma, ie the magnetic sheath 11, which causes a sudden drop in the magnetic induction. The portions of the pipes 21 and 23 located at the level of the outer casing 11 are regions having a high magnetic gradient, that is, regions where the magnetic induction changes greatly.

FIG. 2 shows the electrogram generated in the ion source when the electron cyclotron resonance ion source is optimized. The electric field E is optimum at the resonance points A, B and C.

In practice, the electron cyclotron resonance is optimized at point C when the electric field E reaches its maximum and is perpendicular to the resonance-inducing field and on a cylinder of small radius, ie of the small radius. It is on the second pipe 23.

Further, in the presence of the optimized electron cyclotron resonance, since the preionized plasma generated in the pipes 21 and 23 has a high density, this becomes substantially a conductor and diffuses to the resonance isomagnetic surface 13 and reaches the point B. To reach.
Further, the resonance isomagnetic surface 13 contains high-density plasma and absorbs and reflects electromagnetic waves, so that the resonance isomagnetic surface 13 is a semiconductor from the point B to the point A.

Therefore, from the electromagnetic point of view, the ion source behaves like a coaxial line up to the point A on the magnetic axis 15. This open line is the point where a standing wave exists between points A and 45.

From a more practical point of view, each pipe 23 and 2
The diameters d and D of 1 are optimally fixed by observing the following rules. D-d / 2 = λ / 3

Similarly, the chamber 1 and the resonance isomagnetic surface 13 are formed.
The diameters D 1 and d 2 of are the optimal choices when this rule holds. That is, D-d / 2 = λ / 3

In order to optimize this ion source, in other words, in the case of the electric field E which should be optimized at the points A and B, the important condition regarding the distance between the points A, B and C is not satisfied. I won't. The distance between this point A and B, B and C, or C and A is equal to an integer (n or m) times 1/2 λ of the electromagnetic wave introduced into the ion source.

Therefore, the following equation is obtained. AB = nλ / 2, and AC = mλ / 2 This wavelength λ is a known value from the time when the frequency f of the electromagnetic wave injected by the electromagnetic field generator 3 is known, and the propagation velocity c at the frequency f of the introduced wavelength. be equivalent to.

FIG. 3 is a diagram showing an ion source comprising the apparatus of the present invention, in which the positions of points A, B and C can be optimized.

The ion source shown in FIG. 3 is the same as the prior art ion source, but with the optimization apparatus of the present invention added. This ion source was described at the beginning of the description. All the elements referred to in the description of FIG. 1 are the same as those of FIG.
But they retain the same reference numbers.

An optimization device for optimizing the ion source is shown in FIG. The optimizer consists of a tubular piece 47 known as a magnetic screw. This tubular piece 47 is arranged around the first pipe 21 with a suitable play of about 0.5 mm, which avoids friction with the pipe 21 when the pipe 21 translates with respect to the sheath 11. I am trying. The tubular piece 47 has the same thickness as the outer casing 11 and is provided with a thread 47a around the outer periphery thereof that can be screwed into the tapped portion (11a) of the outer casing 11. The screwing in / returning of the tubular piece 47 on the sheath 11 allows the tubular piece 47 to move.

The tubular piece 47 is made of iron. For this reason, there is a high magnetic gradient at the level of the outer casing 11, and the resonance point C
The position of can be controlled. Actually, the point C is the exterior 1
Almost follows the movement of the tubular piece 47 with respect to 1.

The movement of the tubular piece 47 causes the two dogs to engage two of the four holes 47b in the tubular piece 47.
It is done by a special tool with points. These 4
The two holes 47b are evenly distributed on the outer surface of the tubular piece 47, and are on an axis parallel to the magnetic axis 15. A special tool with two dog points has two opposite radial
By engaging the two holes, the tubular piece 47 can be rotated.

The translation of the tubular piece 47 takes place in the absence of a magnetic field, ie when the ion source is stopped.
In the presence of the magnetic field generated by the solenoid 9, an interaction is established between the tubular piece 47 and the sheath 11. In practice, a considerable magnetic force opposes the translation of the tubular piece 47,
The thread 47a of the tubular piece 47 is replaced by the thread 11a
Ion source exterior 1 by pressing strongly on a
The magnetic continuity within 1 is secured.

However, in order to completely optimize the ion source, the position adjustment of the point C by controlling the tubular piece 47 has to be completed by two adjustments of the tubular piece 47 according to said adjustment. These adjustments allow optimization of the ion source in a continuous manner.

Optimization of the electric field E at point C is obtained by a high gas pressure, which optimizes the ion source in the low ionization charge state. This optimization is determined by first adjusting the position of the tubular piece 47 and secondly the adaptive piston 45. In that case, the first position of point C exists. According to conventional knowledge of the axial magnetic profile of the ion source, points A and B are located by adjusting the current strength in the two solenoids 9. This strength is controlled, for example, by an external power supply that supplies a current that varies from 0 to 1000 amps.

These three adjustments are updated multiple times for increasing gas pressures until an optimization of the ion source in the high ionization charge state is obtained.

According to one embodiment of the ion source according to the invention, the chamber 1 has a diameter of about 6 cm and the introduced electromagnetic wave has a wavelength λ of 3 cm, ie a frequency of 10 GHz. For this ion source, all conditioning has to be performed for electromagnetic powers of 100 watts or less. A skilled operator can optimize this insulation in 5-6 operations. This is within minutes.

[Brief description of drawings]

1 is a schematic cross-sectional view of an ECR ion source according to the prior art.

FIG. 2 is an electric diagram formed in the ion source when the ion source is optimized.

FIG. 3 is a schematic diagram of an ECR ion source optimized according to the present invention.

FIG. 4 is a schematic diagram of an apparatus of the present invention for optimizing the ECR ion source of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 chamber 3 electromagnetic field generator 11 exterior 20 transition cavity 21, 23 pipe 23a transparent part 45 adaptive piston 47 tubular piece 47a, 47b hole

Claims (3)

[Claims] 1. A magnetic structure having a chamber containing a plasma of ions and electrons formed by electron cyclotron resonance, and a magnetic structure having a sheath, the structure surrounding the chamber, A sheath for enclosing a plasma in the chamber by forming two radial and axial magnetic fields, a transition cavity connected to the electromagnetic wave generator, and a transition cavity connecting the chamber and the transition cavity. First and second dielectric pipes having transitions on opposite sides of the sheath, the second pipes producing resonance at a particular point. An ion source using electron cyclotron resonance, comprising means for moving a resonance point in the second dielectric pipe to optimally adjust the position of the resonance point. Ion source by electron cyclotron resonance which is butterflies. 2. The means for moving the resonance point is characterized in that it comprises a tubular piece arranged around the second pipe at the level of the transparent part and movable parallel to said pipe. The ion source according to claim 1. 3. The ion source according to claim 2, wherein the tubular piece is threaded on an outer peripheral portion thereof to form a screw and nut structure together with the exterior.